function getPropertyDescriptor(obj, property) {

     const descriptor = Object.getOwnPropertyDescriptor(obj, property);

     if (descriptor !== undefined)

         return descriptor;

     const proto = Object.getPrototypeOf(obj);

     if (proto === null)

         return undefined;

     return getPropertyDescriptor(proto, property);

 }

​

 function getPropertyOrDefault(obj, property, defaultValue) {

     const d = getPropertyDescriptor(obj, property);

     if (d) {

         if (Object.prototype.hasOwnProperty.call(d, "value"))

             return d.value;

         if (Object.prototype.hasOwnProperty.call(d, "get"))

             return d.get.call(obj);

     }

     return defaultValue;

 }

​

 function getPropertyOrDefault2(obj, property, defaultValue) {

   if (Reflect.has(obj, property)) return obj[property];

   return defaultValue;

 }

​

 class T {

     constructor() {

         this.requiredField = 1;

         this.undefinableField = undefined;

         this.m_requiredProp = 1;

         this.m_undefinableProp = undefined;

     }

     get requiredProp() {

         return this.m_requiredProp;

     }

     set requiredProp(value) {

         this.m_requiredProp = value;

     }

     get undefinableProp() {

         return this.m_undefinableProp;

     }

     set undefinableProp(value) {

         this.m_undefinableProp = value;

     }

 }

 var t = new T();

 t.requiredField = 1;

 t.requiredProp = 1;

​

 class D extends T {}

 var d = new D();

d.requiredField = 1;

 d.requiredProp = 1;